1. Field of the Invention
The invention relates to a spring strut, which has a pneumatic spring with a spring space bounded by a U-type bellows and an oscillation damper with a damping device which can be modified as a function of the support pressure, the bellows riding on an unrolling piston filled to a container of the oscillation damper. In order to modify the damping effect as a function of the support pressure, the spring space is pneumatically connected to the damping device.
2. Description of the Related Art
U.S. Pat. No. 3,399,882 and DE 44 03 196, to which U.S. Pat. No. 5,509,512 corresponds, disclose spring struts in which the U-type bellows is fastened on the container or the cylinder of the oscillation damper and the U-type bellows unrolls on these components. In these designs, the pressure in the spring space acts on a diaphragm, which modifies the valve device or a passage cross section by means of complicated transmission and adjustment elements. Such spring struts are exclusively designed for predetermined damping force variation; once determined, modification or adjustment to the damping force can no longer be undertaken without partial dismantling. A different damping force characteristic demands a modification to components which are not accessible after assembly, so that a subsequent adjustment is very problematic and expensive.
It is also known to arrange easily accessible and variable damping valves externally on the container of the oscillation damper. These valves are easily accessible after removal of the valve housing cap. Such embodiments have a hose conduit between the spring space and the valve device, which hose conduit must be connected both to the spring space by means of a screw connection and to the valve device by means of a further screw connection. These connections are not therefore only expensive to manufacture and assemble, but are also susceptible to external damage.
The object of the present invention is to create a spring strut with adjustment, as a function of the support pressure, of a damping device of the oscillation damper, which spring strut has a simple construction, can be assembled without problem, consists of components which can be manufactured at favorable cost and possesses a high level of operational reliability.
According to the invention, the spring space is pneumatically connected to the damping device by a duct configured without a hose. The duct is integrated into the spring strut and is formed at least in part by the unrolling piston.
The invention provides a simple construction, a connection between the spring space of the pneumatic spring and the damping device which is protected against damage and accessible from the outside, as well as easy and problem free assembly. The duct section integrated in the unrolling piston is formed, for example, by two adjacent support ribs and/or a connection hole, which open into a further duct section. A simple connection between the spring space and the damping device is obtained by providing the unrolling piston with an extension exhibiting the further duct section, which extension can be directly connected to the damping device of the oscillation damper. The extension is preferably embodied as a connecting part, which has a connection mouthpiece, which accommodates a seal and which, by means of the mouthpiece, engages in a connection hole of the unrolling piston. This creates a connection between the spring space and the damping device which is simple, is of favorable cost, can be assembled without problems and is operationally extremely reliable.
A snap connection, between the connection mouthpiece of the connecting part and the connection hole of the unrolling piston, may be provided by sprung tongues each of which has a protrusion at the end of the connection mouthpiece and by this means engages behind the connection hole. This creates a reliable connection by simply pressing the connection mouthpiece into the connection hole. Such a snap connection can be manufactured and assembled at favorable cost and is not released by the internal pressure present in the spring space.
A very compact design of the spring strut is created by arranging the connecting part in a corresponding recess of the unrolling piston and, at least in the region of the unrolling piston, by providing the connecting part with an external surface which is matched to the external contour of the unrolling piston, so that the connecting part is included in the rolling surface for the U-type bellows. By this means, a rolling surface which does not have any interfering edges is created for the U-type bellows.
For simple connection to the damping device, the connecting part is provided with a connection which interacts with a seal. This connection is, for example, embodied as a spigot which forms a plug-in connection with a corresponding hole in the housing cap. If the center line of the spigot and the center line of the hole extend parallel to the center line of the spring strut, it is then also possible to produce the plug-in connection with the damping device at the same time as the unrolling piston, which is provided with the connecting part, is pushed onto the container of the oscillation damper. According to a further embodiment, the spigot forming the connection and the hole in the housing cap have a common center line which extends at right angles to the center line of the spring strut, In this arrangement, the connecting part can be pushed on after the unrolling piston has been pushed onto the container of the oscillation damper, it being also possible to embody the trunnion pushed into the hole of the housing cap with elastic tongues for a snap-in connection.
The accurate positioning of the unrolling piston on the container of the oscillation damper takes place by means of one or more radially outwardly directed protrusions on the container, which interact with corresponding recesses in the unrolling piston. A very simple and cost-saving embodiment is obtained if, for accurate positioning, the housing of the damping device forms the protrusion and the unrolling piston is in contact with this housing by means of a correspondingly matched recess. The unrolling piston is pressed axially downward against the housing by the pressure in the spring space. In order to prevent any possibility of the unrolling piston moving axially on the housing, which can occur during transport, during installation or during operation due to objects lying on the track, axial fixing of the unrolling piston on the container is provided simply and at favorable cost if the housing of the damping device is part of this axial fixing arrangement.
Very simple axial fixing of the unrolling piston on the container, which is produced automatically during the assembly of the unrolling piston on the container of the oscillation damper, is provided by a snap-in connection between these two components. This snap-in connection is formed by at least one snap arm which engages in a corresponding depression or recess in the housing of the damping device, the connection feature of the connecting part being a spigot, which extends parallel to the center line of the spring strut and which engages in a corresponding hole in the housing cap.
Further embodiments, which have simple and easily manufactured fixing arrangements for the unrolling piston on the container are created by the unrolling piston having an axial extension, which is provided with a recess matched to the housing. The fixing takes place by means of a clamp, which is seated on the extension and is arranged below the housing. In a further advantageous embodiment, the unrolling piston has two connecting arms encompassing a cylindrical region of the housing, which connecting arms are connected together by means of a locking screw or a locking pin in contact with the lower edge of the housing.
A design which is simple in construction and can be assembled without problems is obtained if the connecting part is configured in one piece with the housing cap and is permanently connected to the housing of the damping device. In this way, axial fixing of the unrolling piston on the container is also additionally created by means of tea connecting part so that, furthermore, a nicely shaped embodiment of the spring strut is obtained.
In addition, an advantageous design is created by means of a connecting part if this connecting part is first connected to the housing cap of the damping device and the connection with the unrolling piston is produced when it is pushed onto the container. A particularly favorable embodiment is obtained if a push connection is arranged between the connecting part and the acceptance feature formed by the unrolling piston. Connecting parts configured in this way can also be matched without problems to the external contour of the unrolling piston.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.